Stool: Microscopic examination, and culture for isolation and identification of enteric pathogens including ETEC. V. cholerae and S.Typhi will be carried out for four days prior to vaccination. Children who have any of these pathogens isolated from their stool specimen will not be vaccinated since they will confound evaluation of the response to the vaccine. When immunization for the second dose of the vaccine will be carried out (14 days after the first dose) children who have fever or diarrhea will be excluded from the study.